U.S. patent number 4,460,059 [Application Number 06/397,890] was granted by the patent office on 1984-07-17 for method and system for seismic continuous bit positioning.
Invention is credited to Lewis J. Katz.
United States Patent |
4,460,059 |
Katz |
July 17, 1984 |
Method and system for seismic continuous bit positioning
Abstract
The specification discloses a method and system for determining
the position of a drill bit in the earth without interrupting the
drilling operations. In operation, rotation of the drill bit
against the formation being drilled generates coherent acoustical
signals which are recorded at the surface of the earth by a
plurality of spaced detectors. The signals recorded at each of the
different detectors are time shifted relative to each other. These
time shifts correspond to possible locations of the drill bit
within the earth and are controlled to some degree by the length of
drill pipe in the borehole. After the acoustic signals are shifted
in time their coherency is determined. This procedure is repeated
for a number of assumed locations of the drill bit. The drill bit
position is determined to be at the location having the highest
coherency value. In this manner the surface detectors are focused
on precise positions within the earth avoiding interference from
acoustical signals generated at the surface or from the drill
pipe.
Inventors: |
Katz; Lewis J. (Salt Lake City,
UT) |
Family
ID: |
26668525 |
Appl.
No.: |
06/397,890 |
Filed: |
July 13, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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001079 |
Jan 4, 1979 |
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Current U.S.
Class: |
181/102; 175/40;
367/33 |
Current CPC
Class: |
G01V
1/42 (20130101); E21B 47/02 (20130101); E21B
47/0224 (20200501); G01V 2210/161 (20130101) |
Current International
Class: |
E21B
47/022 (20060101); E21B 47/02 (20060101); G01V
1/42 (20060101); G01V 1/40 (20060101); E21B
047/022 () |
Field of
Search: |
;367/14,30,33,56,57,58,59,69,81,86,83 ;181/102,106 ;175/45,40
;340/853,860 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Capon et al., "Short-Period Signal Processing Results for the Large
Aperture Seismic Array", Geophysics, vol. 33, No. 3, (Jun. 1968),
pp. 352-372. .
Niedell and Tanner, Semblance and Other Coherence Measures for
Multi-Channel Data", Geophysics, vol. 36, No. 3, (Jun. 1971), pp.
482-496. .
Lutz et al., "Instantaneous Logging Based on a Dynamic Theory of
Drilling", paper presented at Society of Petroleum Engineers 46th
Annual Fall Meeting, Oct. 3-6, 1971, printed in Transactions, vol.
253, 1972. .
Power et al., "Detection of Hydraulic Fracture Orientation and
Dimensions in Cased Wells", Journal of Petroleum Technology, Sep.
1976, pp. 1116-1124..
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Primary Examiner: Buczinski; S. C.
Assistant Examiner: Kaiser; K. R.
Attorney, Agent or Firm: Banner, Birch, McKie &
Beckett
Parent Case Text
This is a continuation of application Ser. No. 001,079, filed Jan.
4, 1979, now abandoned.
Claims
I claim:
1. A method for locating the position of a continuously rotating
drill bit in a borehole without interrupting drilling operations
comprising the steps of:
continuously rotating said drill bit against the formation being
drilled to generate a drill bit acoustic signal;
positioning an array of seismic detectors at or near the surface of
the earth to detect said drill bit acoustic signal generated by
said continuously rotating drill bit;
determining the approximate depth of said drill bit in the
borehole;
assuming a set of positions for said drill bit as a function of the
approximate depth of said drill bit;
selecting one assumed position for said drill bit and calculating
the travel times for the drill bit acoustic signal generated by
said continuously rotating drill bit from said one assumed position
to each of said seismic detectors;
time shifting the drill bit acoustic signals detected by each
seismic detector relative to a time reference by an amount
corresponding to the calculated travel time of the drill bit
acoustic signal generated by said continuously rotating drill bit
from said one assumed position to said seismic detectors;
correlating the time shifted drill bit acoustic signals for said
one assumed position of said drill bit by calculating a coherency
value representing the coherency of the time shifted acoustic
signals;
selecting other assumed positions in the set of assumed positions
for said drill bit and repeating the steps of calculating the
travel times, time shifting the drill bit acoustic signals and
correlating the time shifted acoustic signals for each assumed
position to obtain a set of coherency values corresponding to the
set of assumed positions for said drill bit; and
comparing the coherency values corresponding to the set of assumed
positions for said drill bit to determine the location of said
drill bit.
2. The method according to claim 1 wherein the acoustic signal
generated by the continuous rotation of said drill bit against the
formation is segregated from other acoustic signals by the steps of
selecting assumed positions for said drill bit, time shifting the
acoustic signals detected by said seismic detectors, correlating
the time shifted acoustic signals and comparing the coherency
values.
3. The method according to claim 1 wherein the steps of time
shifting the acoustic signals, correlating the time shifted
acoustic signals and comparing the coherency values are carried out
by a computer at the well site in real time.
4. The method according to claim 1 wherein the acoustic signal
generated by the drill bit is coherent and has a continuous
waveform.
5. The method according to claim 1 wherein the acoustic signal
generated by the drill bit may be varied by varying the rotational
speed of said drill bit.
6. The method according to claim 1 wherein the steps of selecting
assumed positions for said drill bit, time shifting the acoustic
signals, correlating the time shifted acoustic signals and
comparing the coherency values are performed at discrete intervals
at the well site in real time.
7. The method according to claim 1 wherein the steps of selecting
assumed positions for said drill bit, time shifting the acoustic
signals, correlating the time shifted acoustic signals and
comparing the coherency values are performed continuously at the
well site in real time.
8. The method according to claim 1 wherein the step of correlating
the time shifted acoustic signals is performed by adding and/or
multiplying the amplitude values of the time shifted acoustic
signals.
9. The method according to claims 1 or 8 wherein the location of
said drill bit corresponds to the highest coherency value of the
set of coherency values.
10. The method according to claim 1 wherein said drill bit is
rotated by a drilling rig including a drill string and the depth of
said drill bit in the borehole is estimated as a function of the
known length of the drill string.
11. The method according to claim 1 wherein the depth of said drill
bit in the borehole is determined as a function of the known depth
of geologic boundaries.
12. The method according to claim 1 wherein said seismic detectors
are spaced apart in a two-dimensional array.
13. The method according to claim 12 wherein said array of seismic
detectors includes at least three seismic detectors.
14. The method according to claim 1 further comprising the step of
recording the acoustic signals detected at each seismic
detector.
15. In a drill bit location system for a rotary drilling rig, said
rotary drilling rig including a drill string and a drilling
mechanism to rotate said drill string and an associated rotatable
drill bit to drill a borehole, said drill bit location system
including an array of spaced seismic detectors to detect seismic
signals and signal processing means coupled to said seismic
detectors for processing the seismic signals, a method for locating
the position of said rotatable drill bit in the earth during
continuous rotation of said rotatable drill bit in the borehole,
said method comprising the steps of:
detecting a drill bit acoustic signal emanating from said rotatable
drill bit during continuous rotation of said rotatable drill bit
against the formation being drilled, the drill bit acoustic signal
being detected by said array of seismic detectors;
positioning said array of seismic detectors to obtain phase
differences in the drill bit acoustic signal detected at different
seismic detector positions;
determining a set of assumed positions for said rotatable drill bit
utilizing known information about the approximate depth of said
drill bit;
calculating the travel times for the drill bit acoustic signal from
one of the assumed positions for said rotatable drill bit to each
of said seismic detectors in said array of seismic detectors;
segregating the drill bit acoustic signal from other acoustic
signals detected by said seismic detectors by (1) time shifting the
acoustic signal detected by each of said seismic detectors relative
to a time reference by an amount corresponding to the calculated
travel time of the drill bit acoustic signal from said one assumed
position to said seismic detector and (2) correlating the time
shifted acoustic signals for said one assumed position of said
rotatable drill bit by calculating a coherency value representing
the coherency of the time shifted acoustic signals;
repeating the steps of calculating travel times of the drill bit
acoustic signal and segregating the drill bit acoustic signal from
other acoustic signals for each assumed position for said rotatable
drill bit; and
comparing the coherency values for all assumed positions for said
rotatable drill bit to determine the location of said rotatable
drill bit.
16. The method according to claim 15 wherein the step of
segregating the drill bit acoustic signal from other acoustic
signals is carried out by a computer at the well site in real
time.
17. The method according to claim 15 wherein the drill bit acoustic
signal is coherent and has a continuous waveform.
18. The method according to claim 15 wherein the drill bit acoustic
signal may be varied by varying the rotational speed of said
rotatable drill bit.
19. The method according to claim 15 wherein the steps of
determining assumed positions for said rotatable drill bit,
calculating travel times, segregating the drill bit acoustic signal
from other acoustic signals and comparing coherency values are
performed at discrete intervals at the well site in real time.
20. The method according to claim 15 wherein the steps of
determining positions for said rotatable drill bit, calculating
travel times, segregating the drill bit acoustic signal from other
acoustic signals and comparing coherency values are performed
continuously at the well site in real time.
21. The method according to claim 15 wherein correlation of the
time shifted acoustic signals is performed by adding and/or
multiplying the amplitude values of the time shifted acoustic
signals.
22. The method according to claims 15 or 21 wherein the location of
said rotatable drill bit corresponds to the highest coherency value
of the set of coherency values.
23. The method according to claim 15 wherein the approximate depth
of said drill bit in the borehole is a function of the known length
of the drill string.
24. The method according to claim 15 wherein the approximate depth
of said rotatable drill bit in the borehole is a function of the
known depth of geologic boundaries.
25. A method for locating the position of a continuously rotating
drill bit in a borehole comprising the steps of:
continuously rotating said drill bit against the formation being
drilled to generate a drill bit acoustic signal;
positioning an array of seismic detectors at or near the surface of
the earth to detect the drill bit acoustic signal, said array of
seismic detectors being positioned to obtain phase differences in
the drill bit acoustic signal detected by said seismic
detectors;
determining the approximate depth of said drill bit in a
borehole;
assuming a set of positions for said drill bit as a function of the
approximate depth of said drill bit;
segregating the drill bit acoustic signal from other acoustic
signals detected by said seismic detectors in accordance with the
following steps:
selecting one assumed position for said drill bit and calculating
the travel times for the drill bit acoustic signal from said one
assumed position to each of said seismic detectors;
adjusting the time reference of the acoustic signals detected by
each seismic detector by an amount corresponding to the calculated
travel times for said seismic detector for said one assumed
position of said drill bit;
correlating the adjusted acoustic signals for said one assumed
position of said drill bit by calculating a coherency value
representing the coherency between the adjusted acoustic
signals;
selecting other assumed positions in the set of assumed positions
for said drill bit and repeating the steps of calculating the
travel times, adjusting the time reference to the acoustic signals
and correlating the adjusted acoustic signals for each assumed
position to obtain a set of coherency values corresponding to the
set of assumed positions for said drill bit; and
comparing the coherency values for the set of assumed positions for
said drill bit to segregate the drill bit acoustic signal; and
identifying one of the assumed positions for said drill bit as the
location of said drill bit in accordance with the coherency values
calculated in said segregating step.
26. The method according to claim 25 wherein the step of
segregating the drill bit acoustic signal from other acoustic
signals is carried out by a computer at the well site in real
time.
27. The method according to claim 25 wherein the step of
correlating the adjusted acoustic signals is performed by adding
and/or multiplying the amplitude values of the adjusted acoustic
signals.
28. The method according to claim 25 wherein the step of adjusting
the time reference of the acoustic signals is performed by time
shifting the acoustic signals by an amount corresponding to the
calculated travel times.
29. The method according to claim 25 wherein the location of said
drill bit corresponds to the highest coherency value of the set of
coherency values.
30. The method according to claim 25 wherein said drill bit is
rotated by a drilling rig including a drilling string and the depth
of said drill bit in the borehole is estimated as a function of the
known length of the drill string.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and system for determining
the three dimensional position of the bottom of a borehole and
which permit these positions to be determined continuously or at
discrete intervals as the borehole is advanced without interrupting
the drilling process.
2. Description of Prior Art
In conventional rotary drilling operations the direction and
position of the bottom of a borehole with respect to its surface
location is determined by suspending drilling operations and
lowering suitable tools into the borehole to obtain the desired
information. Time lost from suspending drilling operations to make
these measurements is extremely expensive.
In U.S. Pat. Nos. 2,062,151 and 3,187,345 the drill bit is dropped
several feet to generate a discrete acoustical wave that can be
detected at the surface. The disadvantage in these systems is that
drillers are reluctant to drop the drill bit because of damage that
is likely to occur to the bit. Also, mentioned in U.S. Pat. No.
2,062,151 is the use of elastic waves produced by the action of a
rotary cutting tool on the formation in which it is drilling to
determine the position of the bottom of the borehole.
In actual practice, the elastic waves produced by the action of a
rotary drill bit are quite complex making visual comparisons of
waveforms impractical, especially in the presence of noise
generated by surface equipment and the action of the drill string
rotating against the sides of the borehole. Hence, it would be
practically impossible to visually distinguish waveforms and to
segregate those acoustical signals generated by the drill bit from
those caused by surface noise or the drill string.
SUMMARY OF THE INVENTION
By focusing an array of acoustical detectors which are located at
the surface of the earth on precise positions within the earth, the
location of a drill bit that generates coherent acoustical signals
can be determined. Thus, by focusing detectors on locations
corresponding to a depth within the earth determined by the length
of drill pipe down the borehole, the acoustical signal generated by
the drill bit can be segregated from other acoustical signals that
interfere with the desired signal. In this manner limitations of
the prior art are overcome in this invention.
Accordingly, it is an object of the present invention to provide an
improved method and system for determining the position of the
bottom of a borehole by focusing an array of acoustical detectors
on selected positions within the earth to separate out acoustical
noise signals arriving at the detectors from locations other than
those determined by the length of drill pipe down the borehole.
It is another object of this invention to provide an improved
method of determining the position of the bottom of the borehole
without interrupting the drilling operations.
It is a further object of the present invention to provide an
improved method and system for determining the position of the
drill bit by utilizing coherent acoustical signals generated by
rotating the bit against the formation being drilled and having
such signals detected at the surface by a plurality of spaced
detectors.
In operation, rotation of the drill bit against the formation being
drilled generates coherent acoustical signals which are recorded at
the surface of the earth by a plurality of spaced detectors. The
signals recorded at each of the different detectors are time
shifted relative to each other. These time shifts correspond to
possible locations of the drill bit within the earth and are
controlled to some degree by the length of drill pipe in the
borehole. After the acoustical signals are shifted in time their
coherency is determined. This procedure is repeated for a number of
assumed locations of the drill bit. The drill bit position is
determined to be at the location having the highest coherency
value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a rotary drilling system and a plurality of
spaced seismic detectors located at the surface of the earth and
coupled to a recording system for detecting and recording
acoustical signals generated by the drill bit down hole and hence
near the bottom of the borehole.
FIG. 2 illustrates waveforms detected and recorded by the detection
and recording system of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIGS. 1 and 2, there will be described the rotary
drilling system. Shown is a cross section of the earth 15 with the
earth's surface 16. The numeral 10 designates a derrick located
over a borehole 11 that contains drill pipe 14 and a drill bit 12.
The rate at which the drill bit 12 is rotated varies and may fall
within the range for example of from 30 to 250 rpm. The borehole 11
is indicated as being curved and, therefore, the drill bit 12 is
not always located below the derrick 10. The detecting system in
one embodiment comprises three spaced seismic detectors (geophones)
illustrated at G.sub.0, G.sub.1, . . . G.sub.n and coupled to the
ground for detecting elastic waves generated from the rotation of
drill bit 12 against the formation being drilled and arriving at
the detectors by way of travel paths depicted by arrows P.sub.0,
P.sub.1, . . . P.sub.n. Although only three detectors are illustrat
ed, it is understood that more may be employed. The outputs of the
detectors are applied by way of amplifiers A.sub.0 through A.sub.n
to a recorder 20 which may record the outputs in digital or analog
form. The recorder will show a record of continuous traces
TR.sub.0,TR.sub.1, . . . TR.sub.n corresponding generally to that
shown in FIG. 2.
The detectors G.sub.0, G.sub.1, . . . G.sub.n are spaced apart in a
2-dimensional surface array sufficient for the elastic waves
generated by drill bit 12 to reach the detectors in a manner that
phase differences in the recorded signals can be used to locate the
drill bit 12. Hence, waveforms detected and recorded are compared
to determine phase differences between the signals in order to
determine and compute the position of the drill bit in the earth.
The comparisons and computations may be carried out at the well
site with the use of suitable electronic or digital computing
instrumentation illustrated at 24. Hence, the position of the drill
bit and thus the bottom of the borehole may be determined during
drilling operations either continuously or at discrete intervals as
the borehole is drilled. The detector positions G.sub.0, G.sub.1, .
. . G.sub.n may consist of several acoustical detectors (geophones)
wired together and having a common output designed to attenuate
unwanted surface noise generated from the drilling operations or
from shallow sections of the drill pipe 14 rubbing against the
borehole 11. The drill bit 12 may be coupled and decoupled or
varied in rotational speed to produce variations in the recorded
signal that would enhance the correlation process. The acoustic
signal generated from action of the drill bit 12 on the formation
being drilled consists of continuous and coherent waveforms
containing a suite of frequencies traveling at the same
velocity.
The computation scheme employed in determining the position of the
drill bit relies on having a knowledge of the length of drill pipe
14 down the borehole. With this knowledge the surface detectors
G.sub.0, G.sub.1, . . . G.sub.n can be focused in a sense on
selected positions within the earth controlled by the length of
drill pipe 14 down borehole 11 and the probability that the drill
bit 12 is located in one of the selected positions determined.
Mathematically this can be achieved by the following set of
steps:
First it is necessary to determine several assumed positions for
the drill bit within the earth. Referring to FIG. 1 the position of
the drill bit 12 is limited to those positions within the spherical
coordinate system defined by the angles .theta. and .phi. and by
the approximate length of drill pipe L. Thus, by holding one angle
constant and incrementing the other angle in sequence a set of
possible drill bit locations is determined. These can be
transcribed into Cartisian coordinates by the relationships:
X=L sin .theta. sin .phi.
Y=L sin .theta. sin .phi.
Z=L cos .theta.
Next, the travel times T.sub.0, T.sub.1, . . . T.sub.n along the
seismic paths P.sub.0,P.sub.1, . . . P.sub.n from point X,Y,Z at
the drill bit to the various surface detector positions G.sub.0,
G.sub.1, . . . G.sub.n whose coordinates are defined as
(X.sub.0,Y.sub.0,Z.sub.0), (X.sub.1,Y.sub.1,Z.sub.1), . . .
(X.sub.n, Y.sub.n, Z.sub.n), respectively, are determined. By
having a knowledge of the velocity V this relationship can be
derived for the simple case of a halfspace by
The next step is to time shift the waveforms recorded at each
surface detector by the appropriate travel times T.sub.i for that
detector position and test the coherency between waveforms. This is
achieved by methods of either adding or multiplying the amplitude
values of the shifted waveforms. The above procedure is repeated
for various assumed positions of the drill bit. By introducing the
proper phase shifts to each of the waveforms recorded for all
possible locations of the drill bit and summing or multiplying the
shifted time series one can expect high coherency or power values
whenever the waveforms are aligned for the proper location of the
drill bit and lesser coherency values as one moves away from the
position of the drill bit. In this manner an array of acoustical
detectors located at the surface of the earth can be focused on
precise positions within the earth.
It is understood that variations of the above procedure may also be
employed such as having prior knowledge of the depth of certain
geologic boundaries and when the drill bit enters such a boundary
substituting this depth value for the length of drill pipe in the
above computation. An iteration scheme in which the recorded traces
are shifted relative to each other and coherencies calculated can
also be employed. The travel times associated with the highest
coherency value could be used to determine the location of the
drill bit.
In the past, many people have tried to record the noises made while
the well is being drilled, as an indication of the point at which
the drilling operation is actually taking place. These have always
been unsatisfactory because of the noise generated by the rotation
of the drill pipe along the whole length of the borehole, as well
as noise generated at the surface from drilling operations that
could not be separated from the noise of the drill bit. The
improvement of this invention is in the method of focusing the
array of surface detectors to precise locations within the earth.
These locations are controlled by the length of drill pipe down the
borehole.
It is understood that the invention is not to be limited to the
specific embodiments set forth herein by way of exemplifying the
invention, but the invention is to be limited only by the scope of
the attached claim or claims, including the full range of
equivalency to which each element or step thereof is entitled.
* * * * *